Reset editor intent on new chat and empty editor value (#5991)

This PR solves a bug and implements a minor feature. Well call it bugfix
or feature whatever.

Right now if the intent of chat is set to anything
search/chat/edit/insert and you create a new chat, the intent is not
reset.

why? because the react component is not re-rendered and its
key={n=index}, obviously the index stays 0 when you create a new chat.

So this PR:
1. resets the intent when the input is cleared.
2. resets the intent when the message is changes. 

## Test plan

- change the intent, clear the input, the intent should reset
- change the intent, submit the message, create a new chat, the intent
should reset.

## Changelog

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vscode/webviews/chat/cells/messageCell/human/editor/HumanMessageEditor.tsx

@@ -119,6 +119,18 @@ export const HumanMessageEditor: FunctionComponent<{
         initialIntent || (experimentalOneBoxEnabled ? undefined : 'chat')
     )
 
+    useEffect(() => {
+        // reset the input box intent when the editor is cleared
+        if (isEmptyEditorValue) {
+            setSubmitIntent(undefined)
+        }
+    }, [isEmptyEditorValue])
+
+    useEffect(() => {
+        // set the input box intent when the message is changed or a new chat is created
+        setSubmitIntent(initialIntent)
+    }, [initialIntent])
+
     const onSubmitClick = useCallback(
         (intent?: ChatMessage['intent']) => {
             if (submitState === 'emptyEditorValue') {